SIMATIC Industral Software - Tools for configuring and programming ...

STEP 7 Basis
Structured programming
STEP 7 Basis is the universal programming software for
configuring and programming SIMATIC controllers.
The software supports the user throughout all phases of
automation solutions – from the creation process to plant
failure diagnostics.
The essential characteristic of SIMATIC software and therefore
– in addition to STEP 7 Basis – STEP 7 Professional is its clear
structure.
In the case of comprehensive programs, it is recommended
and sometimes necessary to divide the program into individual
program sections. The program sections should be program
parts that are self-contained and that have a technological or
functional correlation. These program parts are called program
blocks. A block is a part of the user program that is defined
by its function, structure or application.
Elements of a user program
User programs consist of the following elements:
■ Organization blocks (OB)
Organization blocks determine the structure of user programs.
They represent the interface between the operating
system and user program. They control the start-up behavior
of the automation system, cyclic and interrupt-driven
program execution and fault handling.
■ Function blocks (FB), Functions (FC)
- Function blocks are code blocks which contain the actual
program. They have an assigned data block in which the
input and output parameters as well as static data are
stored. Thus the FBs can maintain the processed values
throughout several cycles.
- Functions have no assigned data block; when called, they
always require current input values. They supply their
function result after every call.
- FBs and FCs can be self-programmed. The display of selfprogrammed
blocks can also be suppressed. This is of
interest, for example, to machine manufacturers to
protect their know-how. FBs and FCs are therefore represented
as blackboxes, since the user does not need to
know how their functions were implemented.
Libraries with special, pre-generated blocks that only
need to be interconnected, are available as an option,
for example, IEC functions, controllers and blocks for
converting SIMATIC S5 and 505 programs.
6 Standard tools
Savings potential
■ Even comprehensive programs can be programmed in
a clear manner.
■ Third parties that access structured programs for
service, maintenance or a later modification are better
able to understand and work with the program.
Program testing may be performed in steps.
■ Program sections can be standardized and re-used.
■ Data blocks (DBs)
Data blocks are data storage areas that contain user data.
They can be assigned to individual function blocks or the
complete project.
■ System functions (SFCs) and system function
blocks (SFBs)
Some functions that are repeatedly required are integrated
into the operating system of the S7-CPUs and can be called
from there. Some of these functions are, for example, communication
functions, clock functions and operating hours
counter, or the transfer of data records. The system
functions/system function blocks are supplied as a library
with STEP 7 for offline programming.
Structure of a user program